The use of recycled office waste papers as a precursor source for paper making fibers has become increasingly popular. Recyclable office waste paper often contains ink and laser jet print particles. The latter actually exist as a multiplicity of particles or carbonized specs along the waste paper surface. The former may be described as comprising a mixture of pigment or organic dye, binder and solvent. Of course, in order to recycle such office waste, the ink, including laser print particles, must be removed in order to provide high quality pulp stock for production of high brightness papers.
Traditionally, deinking is accomplished with chemical additives and a plurality of mechanical process steps including the sequential steps of thickening the pulp, dispersing the ink particles in the thickened pulp in a kneading machine or the like, followed by diluting the kneaded pulp. Then the pulp is forwarded to a flotation cell where the dispersed ink particles are separated via air froth flotation or the like on the surface of the pulp slurry.
The aforementioned deinking processes normally contemplate usage of a repetition of the thickening, dispersing, and flotation steps. This accordingly presents an imposing capital expenditure especially with regard to the thickening (i.e. washing) machines since these are large machines, requiring excessive floor space, and are expensive to purchase. The same detriments exist for the dispersing step since the performance of these steps again requires expensive equipment.
U.S. Pat. No. 4,668,339 (Terry) discloses a process for dry deinking of secondary fiber sources wherein air dry secondary fiber batches are shredded to produce discrete fibers and fines. The fines include ink bearing fines or ink particles which are "dry" separated from the fibers via vacuum/screen arrangements. Additionally, wet deinking or cleaning steps may be interposed between this dry shredding and the subsequent pulping of the fibers in an aqueous slurry.
Despite the efforts of the prior art, there remains a need for a process for deinking used office waste paper that will minimize the need for employment of successive thicken, disperse, flotation steps so that capital expenditure for this equipment will accordingly be minimized.
A more specific need exists for a deinking process in which pulping and ink dispersion may be achieved simultaneously by use of the same equipment so that pre-pulping treatments such as those taught by the '339 patent supra. may be eliminated.